Multirange extensometer



Dec. 11, 1951 Filed June 23, 1950 75 Recorder L. K. HYDE MULTIRANGEEXTENSOMETER FIG.

2 SHEETS-SHEET l INVENTOR LAWRENCE K. HYDE ATTORNEY Dec. 11, 1951 K.HYDE I MULTIRANGE EXTENSOMETER Filed June 23, 1950 2 Sl-IEETSSI-IEET 2INVENTOR LAWRENCE K. HYDE if fq ATTORNEY V Patented Dec. 11, 1951MULTIRANGE EXTENSOMETER Lawrence K. Hyde, Washington, D. 0., assignor toBaldwin-Lima-Hamilton Corporation, a corporation of PennsylvaniaApplication J une 23, 1950, Serial N 0. 169,924

Claims. (Cl. 73-88.5)

This invention relates generally to motion sensitive devices and moreparticularly to extensometers for determining strain of specimens undertest in a materials testing machine and it is one object of my inventionto provide an improved dual type motion sensitive device one applicationof which is as a dual extensometer whereby an essentially continuousrecord can be made at high magnification through the clastic portion ofthe specimen and at low strain magnification through the plastic portionof the test specimen and up to failure thereof.

A further object is to provide an improved extensometer for the elasticand plastic ranges that is relatively simple in construction, operationand maintenance, is relatively economical for a device of this type andcan be readily applied to specimens with minimum time, eifort orcomplications.

Various extensometers have been heretofore proposed and used fordetermining low and high magnifications but these had to be used in amanner that produced a discontinuous record between the elastic andplastic ranges, and in some circumstances one specimen had to beemployed for theelastic range and another specimen for the plasticrange, while still other of these prior devices were similarly deficienteither functionally, structurally or economically.

Other objects and advantages will be more apparent to those skilled inthe art from the following description of the accompanying drawings inwhich:

Fig. 1 is a perspective of a portion of a materials testing machine withmy improved dual type extensometer shown as applied to a tensionspecimen;

Fig. 2 is an enlarged transverse section taken substantially in theplane of lines 2-2 of Fig. 1;

Fig. 3 is a section taken substantially in the plane of lines 3-3 ofFig. 1;

Fig. 4 is a fragmentary perspective showin the extensometer of Fig. 1with adaptors for applying the extensometer to a cylindrical type ofspecimen; and

Fig. 5 is a perspective of my dual type extensometerwith adaptors toapply either a different high range magnification or a third range ofmagnification in case such should be desired.

In the particular embodiment of the invention disclosed in Fig. 1, Ihave shown my improved extensometer applied to a strip type specimen Iheld in suitable upper and lower grips 2 and 3 which in turn are mountedin upper and lower testing machine crossheads 4 and 5. These crossheadsare respectively mounted on a pair of loading columns 6, only one ofwhich is shown, and on a pair of load sensitive columns 1, only one ofwhich is shown. Inasmuch as the testing machine per se is wellknown,further detailed description thereof is not necessary. I

The extensometer includes a vertical base plate [0 supported upon ahorizontal bar II which, as'shown in Fig. 5, is longitudinallyextensible as well as being rotatably adjustable, the inner end of thesupporting arm ll having a bracket l2 adapted to be releasably clampedon the column 1 for adjustment in any position along its length. Asshown in Fig. 1 a pair of guideways l3 are formed on base plate 50 toreceive vertically slidable upper and lower blocks I4 and I5. An upperextensometer arm I5 is pivotally supported at I! on slidable block l4while a link I8 is pivotally connected at l9 to the arm and at 20 tobase plate [0. Similarly, a lower extensometer arm 2! is pivotallyconnected to block l5 and to base plate in through a link 22. The outerends 23 and 2d of these extensometer arms freely rest downwardly uponsuitable gage heads 25 and 26 removably clamped to specimen I and spacedapart thereon a desired gage length distance.

A high magnification jstrain sensitive device 21 comprises preferably anelectro magnetic motion responsive device of the type shown in PatentNo. 2,427,866 or any equivalent electrical strain sensitive impedancedevice. As shown in Fig. 3, this device includes a plurality ofelectrical coils 30 rigidly secured to the lower exin core 3 I, serve asa limit stop for upward movement of the core by the nuts engaging theunderside of arm 2|. A low strain sensitive device 34 similar to 21 ismounted adjacent the pivotal end of the extensometer arms. Thissensitive device, as shown in Fig. 2, has its coils 35 secured to slideblock l5 while its core 35 is formed on a screw 31 adjustably mounted ona lug 38 of slide block M. A lower screw 39 is adapted to pre-set thelowermost position of slidingnblock I5 and, accordingly, that of coils35.

The two strain sensitive electrical devices 2? and 34 are connected bysuitablecables 40 and 4| to a sequence switch' 42 having a common. setof wires 43 which lead to a suitable recorder such, by way of examplebut not of limitation, as shown in Patent 2,451,757. Further descriptionin this present application of this recorder and its mode of operationto the sensitive elements 2'! or 34 will not be necessary in view ofthis patent.

In Operation-After the specimen gage supports 25 and-26am clamped uponthe specimen, the arm II and base plate It are positioned on screw I sothat extensometer arms 16 and 2| are substantially horizontal and restfreely upon the gage clamps. The position of the core of the lowmagnification sensitive device 34 is then pre-set by adjustment of screw31', Fig. 2, so that the relationship of the position of this core tothat of the high magnification sensitive element 2'! is such that whensequence switch 42 shifts the extensometer from high magnificationelement 21 to low magnification element 34 there will be a substantiallycontinuous :recording. It is believed tobe clear that highmagnification, of the relatlvely small strain of the specimen during itselastic range, is effective for the reason that the moment arm from thepivot links l8 and 22 to element 21 is of considerable length, whereaslow magnification during the relatively large strain of the specimenduring its plastic range results from the proportionately smaller momentarm from links l8 and 22 to element 34. It is also clear from theparticular nature of the sensitive elements 21 and 34 that during thelarge elongation of the specimen in its plastics range, no damage canresult to either of the sensitive elements as the core 36, Fig. 2, canfreely move while, as shown in Fig. 3, the pointed pin 33 may readilyseparate from its'core 3|. Also the foregoing arrangement permits theextensometer to remain on the specimen clear through iailure thereof.

Hence it is seen that I.have provided extremely simple, yethighlyaccurate, sensitive and responsive extensometer having multiplemagnification ranges as well as being easily and readily attached to aspecimen.

In the modification shown in Fig. 4 the ends of the extensometer arms l6and I l have had its strip type specimen extensions 23 and 24, Fig. I,removed and a pair of U-shaped extensions 48 and 49 substituted, thesevarious extensions being readily attached or removed by screws such asThe ends of the U-shaped extensions rest upon pins 5! of cylindricaltype gage heads 52 and 53 which are particularly suited for acylindrical specimen 54 in distinction to the strip specimen I.

The modification of Fig. 5 is adapted for very long gage lengths inwhich case thehigh magnification sensitive element 55 is mounted betweenextensions 55 and 51 of the extensometer arms I6 and 2!. In order tomaintain the extensometer arms substantially parallel while stillpermitting an exceptionally long gage length to be employed on specimen58, a link 59 may be pivotally connected to the upper-gage point headand provided with a slot Ell at its lower end to receive the finger ofarm 56. The operation of Fig. 5 is the same as described for Fig. 1except that the sequence switch would be connected to elements 55 and2'! or to 55 and 34.

From the foregoing disclosure of the several modifications, it is seenthat I have "provided a very eiiective, highly compact, and accuratemultiple range magnification extensometer that is relatively simple andeconomical, as well 'asbeing easily and readily applied to specimens.

It will, of course, be understood by those skilled in the art thatvarious changes may be made in the construction and arrangement of partswithout departing from the spirit of the invention as set forth in theappended claims.

I claim:

1. An extensometer for determining strain in the elastic and'plasticranges of a specimen, comprising, in combination, a pair of extensometerarms pivotally supported at one end thereof and their other ends beingsupported by the specimen whereby the arms at varying points along theirlength move relative to each other in proportion to the distance of saidpoints from the pivotal ends of i said arms, a motion responsive deviceconnected to said arms at one point thereof so as to effect a givenmagnification suitable for the elastic range of the specimen, a secondmotion responsive device also connected to said arms at a point betweenthe pivoted ends of said arms and said other motion responsive device sothat a smaller degree of magnification can be effected for the plasticrange of the specimen, and means for obtaining a substantiallycontinuous response through the elastic and plastic ranges of thespecimen by rendering said motion responsive devices sequentiallyoperable.

2. The combination set forth in claim 1 further characterized in thatone of said motion responsive devices includes relatively movableportions, one of which is supported by one of said arms and the other ofwhich has separable engagement with the other of said arms whereby uponan excessive amount of movement between the arms, the said engagement isdiscontinued without damage to the motion responsive device.

3. The combination set forth in claim 1 further characterized in thatone of said motion responsive devices has relatively movable portionsfreely separable from each other and one of which is connected to theone of said arms and the other of which is connected to the other arm.

4. The combination set forth in claim 1 further characterized in thatthe motion responsive devices have electro magnetic coils supported byone of the arms and cores freely movable within the respective coilsconnected to the other of the arms.

5. Thecombination set forth in claim 1 further characterized in that themotion responsive devices have electro magnetic coils supported by oneof the arms and cores connected to the other of the arms and freelymovable within the respective coils, and means for relativelypositioning the cores and coils of the respective responsive devices sothat the effectiveness of one motion responsive device will besubstantially continuous with that of the other responsive device whensaid devices are rendered sequentially operable.

LAWRENCE K. HYDE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,431,638 Dowling Oct. 10, 19221,912,213 Nicolson May 30, 1933 2,176,016 Sivertsen Oct. 10, 19392,180,175 Sivertsen Nov. 14, 1939 2,305,816 Sonnberger Dec. 22, 19422,387,496 Cornelius Oct. 23, 1945 2,393,669 Wheaton Jan. 29, 1946

